1. Field of the Invention
Generally speaking, the present invention pertains to the formation of prosthetic dental preforms. More specifically, it is directed to improved methods of producing semi-finished dental porcelain prosthetic crowns and the like.
2. Description of the Prior Art
It is customary practice in the dental field to produce artificial or prosthetic dental preforms, such as crowns and the like. Dental technicians and dentists will select a semi-finished tooth which generally meets the requirements of the dental patient and, thereafter, attempt to fit the preform on a member so as to become a part of a dental appliance, such as bridges and the like. Porcelain is added, as necessary, to achieve the desired shape and color.
The usual technique for producing these preforms can be generally characterized as comprising several rather lengthy steps involving many manual operations. Some of these steps involve building-up and sculpturing a prostheses by hand to simulate the replaced tooth in size, shape and color. It is pointed out that such technique, besides involving several tedious steps often requiring high level skills, also suffers from the shortcoming that it is time consuming. Apart from the foregoing drawbacks, such known technique is also economically limited insofar as only a few of the custom-made prostheses can be produced in any given period of time.
One known material used for producing semi-finished dental preforms employs a dental porcelain mixture including a binder compound which can subsequently be vitrified. In practice, porcelain is highly desirable as a material for prosthetic tooth components since it provides for extra hardness and improved aesthetics. Porcelain more satisfactorily withstands normal use and even abnormal use without failure or appreciable wear. It will be understood that failure of the prosthetic tooth component would cause unnecessary hardship to the patient. Owing, however, to the chemical and physical properties of such types of porcelain as is customarily used in this field, it has been determined from practice that such porcelain is a relatively difficult substance to work with, particularly from the dental standpoint of exactly reproducing numerous custom-made artificial prostheses. It should be pointed out that in the dental field the term dental porcelain is generally used to describe a low alumina ceramic mixture including binder before it is fired or vitrified. Once, however, the ceramic mixture is vitrified it then becomes what is generally regarded as porcelain material.
One known technique used for forming dental porcelain preforms utilizes an appropriate type of ceramic powder mix in conjunction with a suitable liquid binder which are thoroughly admixed into a paste. The paste is molded into the approximate form of a finished crown tooth, for instance, with allowances for porcelain shrinkage. Conventionally, body porcelain and incisal porcelain which go into forming the preform are suitably placed in appropriate locations in a flexible mold. Excess moisture is removed and the noted paste material is dried by heating at a temperature which is sufficiently high in magnitude to burn out or evaporate such excess moisture as well as set the binder material. In such usual process, the removed dried product is then baked or pre-fired to a hard concretious state but, however, is not vitrified. However, the binder leaves undesirable porosity and color.
Exemplary of other known approaches for manufacturing artificial tooth components are generally described in the following U.S. Pat. Nos.: 1,599,084, 1,868,425, 2,584,109, 2,317,103, 2,332,537, 2,333,833, 2,345,305, 2,368,816, 2,491,097, 2,514,076, 2,654,949, 2,703,435, 3,789,910, 3,766,650 and 3,621,576.
Other long recognized problems generally encountered in forming prosthetic dental porcelain preforms is the fact that the accuracy and uniformity of large quantities of molded products vary. Since the formation of accurately and uniformly produced semi-finished preforms varies known processes are rendered less than entirely successful. Also, it has been ordinarily experienced that a known method for forming porcelain preforms is not successful in terms of repeatability, as well as produces preforms which are lacking in sufficient strength for the intended purposes, inter alia, hand carving. Moreover, another significant disadvantage generally associated with heretofore known practices in this field is the fact that the labor costs attendant with the manufacture are relatively high.
Although it has been known to injection mold ceramic materials such as generally described in U.S. Pat. No. 2,964,245, such described process would be unsuitable for purposes of injection molding ceramic materials for dental preforms which have relatively small dimensions and desired color and translucency requirements.
Based upon the preceding considerations regarding the aforenoted contemporary approaches relating to the formation of semi-finished porcelain, prosthetic preforms, it is quite apparent that they are not as economically produced or as reliably consistent as could otherwise be obtained, since with ceramics it is extremely difficult to reliably obtain accurate and uniform preforms particularly whenever producing large numbers of such preforms on a commercial scale. Moreover, the strength of the preforms produced by such methods are inconsistent and, in general, not as high as could otherwise be produced. Additionally, the overall labor costs involved in producing dental preforms are disadvantageous since they are relatively high.